Field
Embodiments of the present disclosure generally relate to downhole sensing and, more particularly, to pressure sensing assemblies in tubing that are insensitive to mechanical loads on the tubing, other than the pressure to be measured.
Description of the Related Art
The world's reservoirs are aging. This translates to increased water production and gas coning, increased lifting costs, expensive treatment of produced water, and high cost of deferred or lost hydrocarbon production. Hence, it is becoming increasingly important to accurately measure and understand conditions inside a well, reservoir, or field. Downhole sensing offers measurement near the areas of interest—e.g., near the wellbore or reservoir—and thus offers potential for higher quality data, more insight across a sandface, and measurement of parameters that are not available on the surface. This information can be used to optimize production, locate water or gas coning, manage fractures or fluid movement in the reservoir from events or disturbances, etc.
Various types (e.g., optical) of sensors may be used for sensing pressure and/or temperature in production tubing located in a wellbore completion for producing hydrocarbons. Traditional tubing strings, in which multiple lengths of tubing are coupled together, or coiled tubing may be deployed in the wellbore completion. In coiled tubing deployments, a length of tubing, which may be of a length appropriate for the depth of the completion, may be spooled onto a take-up reel. During installation, the tubing can be straightened and, using an injector head, can be run into the completion. Because coiled tubing is meant to be spooled onto and unspooled from a reel, the diameter of a coiled tube may be less than the diameter of traditional production tubing.
Several challenges exist with constructing sensors for use in production tubing, especially for coiled tubing deployments. One of these challenges is that the sensor may be subjected to unknown external mechanical loadings such as tension, bending, torsion, and external pressure once the sensor is installed downhole. If the pressure sensing mechanism of the sensor is not properly isolated from its outer shell component, the pressure response of the sensor under the external mechanical loadings will deviate from that obtained during calibration of the sensor under lab conditions. The deviation is dependent on the external loading conditions and can lead to high error in the measured pressure, thus rendering the sensor inaccurate.
There is therefore a need for techniques and apparatus to accurately measure pressure downhole and in other applications while avoiding the introduction of inaccuracy caused by extraneous mechanical loads noted above.